Metal mould for making a frozen confectionary product and a method for making the mould

ABSTRACT

A metal mould for making a frozen confectionery product is made of a titanium-containing materials, the mould being produced by cold-working a sheet-formed blank, either by deep-drawing or by pressing two half shells which are subsequently welded together. By using titanium for the ice lolly moulds, it is possible to avoid the use of poisonous inhibitors, without any risk of corrosion on the moulds. There is a considerable risk of corrosion on the moulds as the moulds used in the production of frozen confectionery products are subjected to freezing baths with strong saline solutions. When using titanium material for making the metal moulds, it is further possible to perform stress-relieving annealing at a lower temperature than was formerly possible when the moulds were made of stainless steel.

BACKGROUND OF THE INVENTION

The present invention relates to a metal mould for use in the productionof a frozen confectionary product, preferably ice lollies.

It is generally known that frozen confectionary products are produced inmetal moulds, so-called freezing pockets. Such metal moulds wereoriginally made from copper alloys, but for very many years they havebeen made from stainless steel.

When making the frozen confectionary product, a large number of mouldsare led through a freezing bath for freezing the confectionary productand afterwards through a defrosting bath for freeing the frozen productfrom the mould walls. A large number of moulds are firmly mounted inplates, which form sections in the installation. An installation inwhich the moulds are placed may be constructed as a rotatinginstallation with the freezing bath and the defrosting bath arranged incircular segments. The installation may alternatively be constructed asan installation in which the moulds are led through freezing anddefrosting baths which are arranged on a line. When passing through thebaths, the moulds are exposed to a temperature difference from down toapprox. -55° C. to a temperature of up to about 30° C.

The freezing bath normally comprises a calcium chloride solution (CaCl₂saline solution). In these saline solutions there will be a considerablerisk of corrosion on the moulds. If just one mould in a section has acorrosion hole, it will be necessary to replace the whole section. Thisinvolves substantial expenses.

Therefore, in order to reduce the corrosion, inhibitors have been usedin the freezing bath. A generally used inhibitor has been sodiumbichromate (Na₂ Cr). This inhibitor will form a protection layer on allsurfaces which contact the saline solution. The inhibitors are difficultto work with as they irritate the skin. Besides there is a health riskif the inhibitor or the saline solution is allowed to penetrate into theconfectionary product through corrosion holes.

In certain cases, owing to requirements from the authorities or internalrequirements, it is impossible to use inhibitors because of the healthrisk involved in using these poisonous substances. In such casespremixed saline solutions are used in the freezing bath instead. Due tothe absence of the inhibitor, however, it will be necessary to maintainpH within very narrow limits of between approx. 8.5 and 9.0 in order toavoid serious corrosion on the moulds and the other parts of theinstallation with which the saline solution comes in contact. Even veryshort periods with pH beyond the above-mentioned limits may give rise toserious corrosion which necessitate replacement of one or severalsections. Thus it is necessary to perform a constant supervision and addpH-adjusting agents if no inhibitors are used.

It has been commonly known in the defrosting bath to protect the mouldsagainst corrosion by using a corrosion plug, e.g., of anodized zinc. Ithas been necessary to inspect this corrosion plug frequently and makereplacements in order to avoid corrosion of the moulds.

A further risk of mould corrosion may be caused by current failures in aplant. Thus, it has been essential that the moulds and other parts of aninstallation were grounded correctly. Such correct grounding may incertain cases be difficult.

Thus, the attempts that have been made until now to avoid corrosion ofmetal moulds have only been directed towards adaptation/modification ofthe involved fluids, inhibitors, etc., in the freezing bath and thedefrosting bath.

Although metals which are very resistant to corrosion have been knownfor years, these have not been used so far because of difficultiesrelated to manufacturing, which involves difficult shaping and welding.Thus, until now it has not been considered a realistic and practicaloption to use other metals which will give the metal moulds a longerlife under subjection to the above-mentioned fluids.

It is the object of the present invention to remedy the drawbacks ofknown metal moulds by disclosing a new metal mould and a method formaking such mould.

SUMMARY OF THE INVENTION

According to the present invention, the metal moulds are made oftitanium.

The mechanical characteristics and methods of working titanium materialshave been known for many years and are described thoroughly in a greatdeal of literature. Among other things, it appears from this literaturethat titanium materials are difficult to pressform and practicallyimpossible to deep-draw. As moulds have been manufactured either bypress forming or by deep-drawing until now, titanium has consequentlynot previously been used.

Titanium has a high affinity to oxygen and a protecting layer oftitanium dioxide will form rapidly, providing effective protectionagainst corrosion of the underlying metal. Thus, the titanium moulds,i.e., which have titanium at an outer surface thereof, will be resistantto the fluids used in freezing baths and defrosting baths in productioninstallations. When using titanium moulds, it is possible in anadvantageous manner to avoid the use of the noxious/poisonousinhibitors, and the life of titanium moulds will consequently beconsiderably longer than that of traditional moulds of stainless steeleven though no inhibitors are used. Furthermore, there will not be asstrict requirements as to maintaining the pH value.

In the method according to the invention for making a metal mould oftitanium, the mould is made by cold-working a sheet-formed blank.

The cold-working may either be performed by pressing two half shellswhich are welded together, or by deep-drawing performed in severalsteps.

Such cold-workings are also used in conventional manufacturing of mouldsof stainless steel. After the cold-working of a sheet-formed blank,stress-relieving annealing must be performed. For stress-relievingannealing stainless steel it has been necessary to use high temperaturesof approx. 1040° C. The stress-relieving annealing must be performed atthese high temperatures due to the fact that during the cold-workingsome austenitious steel is transformed into ferritious steel, whichresults in a shorter life owing to less resistance to corrosion. Thus itis necessary to perform a stress-relieving heating/annealing in order totransform the ferritious steel into austenitious steel in order toobtain sufficient resistance to corrosion in the moulds.Stress-relieving annealing must be used both in press forming anddeep-drawing of moulds made of stainless steel.

It is well known that titanium has a high affinity to other metals and,therefore, has a tendency to stick to a pressing tool during forming.However, surprisingly it has turned out to be possible, by an adequatepressure speed and effective lubricating, not just to press half shellsbut also to perform a deep-drawing. It has proven possible to usepressure speeds corresponding to the pressure speeds for steel, subjectto an adequate lubricating of tools. The deep-drawing may be performedin several steps in order to obtain a total drawing ratio D:d of 6 to10, at a drawing ratio of up to 2.5-2.6 in each step that is necessaryfor moulds for the production of frozen confectionary products.

The cold-working performed also requires stress-relieving annealing.However, for titanium this may be performed at a considerably lowertemperature and thus at considerably lower costs. Thus, it is possibleto perform the stress-relieving annealing of titanium at temperatures ofbetween 650° C. and 700° C. or even as low as temperatures of between450° C. and 550° C. At these temperatures the duration may last between20 minutes and 1 hour, preferably between 30 and 40 minutes. In thismanner a stress-relieving annealing is achieved which allows furtherdeep-drawing, which is preferably performed in 5-8 steps.

In stress-relieving annealing titanium there is no risk of formations ofinternal structures which reduce the resistance to corrosion such as isthe case for stainless steel.

A large number of different types of commercially available titaniummaterials may be used in the manufacture of moulds according to theinvention. Examples of titanium materials that may be mentioned arevarious types of commercially available pure titanium marketed by IMITitanium Limited, IMI 110, 115, 125, 130, 155, and 150. Other examplesof titanium alloys from the same manufacturer are IMI 260 and263, whichhave an improved resistance to corrosion. Other usable titanium alloysare IMI 230, 318, 367, 550, 551,685, 829, and 834. It is also possibleto use titanium material sold by AVESTA Stainless Inc. An example oftheir titanium materials is ATi24, which is particularly suitable fordeep-drawing. Alternatively, one may use ATi30, ATi35, and ATi24PD, thelatter of which is particularly resistant to corrosion. Another exampleof a commercially available titanium material is ASTM-B 265 grade 1.

For lubricating one may use any lubricants known in the art for use indeep-drawing, e.g., lubricants having a viscosity of between 4 and 5cSt.

It is possible to use deep-drawing press tools with different profiles.Thus, one may use round-headed tools, flat-headed tools, tolls with acircular cross-section, a square cross-section or other types ofcross-sections known for confectionary moulds.

The thickness of the initial sheet-formed blank item varies depending onthe individual mould. However, it will be possible to use a sheet havingan initial thickness of between 0.6 and 1 mm, preferably 0.8 mm, for themanufacturing of prevailing confectionary moulds.

DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to an example whichis given in combination with FIGS. 1-7 which depict a deep-drawing insix steps.

A round blank 1 is shown in FIG. 1 and is manufactured from ASTM-B 265grade 1 titanium. A lubricant with a viscosity of 4.5 cSt. is used forthe drawing in each step, and after each drawing a stress-relievingannealing is performed at 650° C. with a heating time of 30 minutes.

In the first drawing, which is illustrated in FIG. 2, a drawing ratio of2.5 is used to form a cup-shaped blank 2 having a bottom 3 and asubstantially cylindrical wall 4, which are connected by an edge area 5.

In step two, which is illustrated in FIG. 3, a drawing ratio of 1.5 isused, and the height of the substantially cylindrical wall 4 isincreased.

In step three, which is illustrated in FIG. 4, a drawing ratio of 1.5 isused again to form a first recess 6 in the cylindrical wall 4.

In step four, which is illustrated in FIG. 5, a drawing ratio of 1.5 isused to form another recess 7 in the cylindrical wall 4.

In step five, which is illustrated in FIG. 6, a drawing relationship of1.3 is used to form a third recess 8 in the cylindrical wall 4. Afterthe fifth drawing, the confectionary mould is completed in its finaldesign 9. A drawing ratio cannot be said to exist in this step becausewhat is performed is actually a smoothing of the formed recesses 6, 7and 8. After completion of the confectionary mould 9, which isillustrated in FIG. 7, a final stress-relieving annealing is performed,which is also performed at 650° C. and a heating time of 30 minutes.

For the sake of good order it is noted that the drawing only illustratesone single example and that the invention may be realized using manyother types of titanium materials and for the manufacture ofconfectionary moulds having other designs than that of the finishedconfectionary mould 9 shown in FIG. 7

I claim:
 1. A metal mould for use in the production of a frozenconfectionery product, said metal mould comprising a hollow mouldelement which defines an inner surface facing a hollow interior of saidmould element and an exterior surface, said mould element consisting ofa titanium-containing material at its exterior surface for resistance tocorrosion by chemicals in a freezing bath through which said mouldelement is passed.
 2. A mould according to claim 1 which has beenmanufactured in one piece by deep-drawing.
 3. A mould according to claim1, which has been manufactured from two pressformed half shells whichhave been welded together.
 4. A mould according to claim 1, which hasbeen stress-relief annealed at a maximum temperature of 650°-700° C. 5.A method for making a metal mould, said metal mould comprising a hollowmould element which defines an inner surface facing a hollow interior ofsaid mould element and an exterior surface, said mould elementconsisting of a titanium-containing material at its exterior surface forresistance to corrosion by chemicals in a freezing bath through whichsaid mould element is passed, said method comprising providing asheet-formed blank which has titanium-containing material at oneprincipal surface thereof and cold working said blank to form said metalmould.
 6. A method according to claim 5, wherein the cold-workingconsists in deep-drawing in 5 to 8 steps, and that the blank isstress-relief annealed after each drawing.
 7. A method according toclaim 5, wherein the cold-working consists in a press forming of twohalf shells, said two half shells are welded together to form thefinished mould, and the mould is stress-relief annealed.
 8. A methodaccording to claim 6, wherein the stress-relief annealing is performedat a maximum temperature of 650°-700° C. for a period of between 20minutes and 1 hour.
 9. A method of making a frozen confectionery productwhich comprises the steps of providing a hollow mould having an outersurface made of a titanium-containing material, delivering aconfectionery product into said mould, and passing said mould withconfectionery product through baths containing a freezing agent and adefrosting agent to provide said frozen confectionery product in saidmould, said titanium-containing material resisting corrosion.
 10. Amethod according to claim 9, wherein said titanium-containing materialis a titanium alloy.
 11. A method according to claim 9, wherein saidtitanium-containing material is pure titanium.
 12. A metal mouldaccording to claim 1, wherein said titanium-containing material is atitanium alloy.
 13. A metal mould according to claim 1, wherein saidtitanium-containing material is pure titanium.
 14. A mould according toclaim 4, which has been stress-relief annealed at a maximum temperatureof 450° to 550° C.
 15. A method according to claim 8, wherein saidstress-relief annealing is performed at a maximum of 450° to 550° C. forbetween 30 and 40 minutes.